1. Field of the Invention
This invention is in the field of joining pressure pipe, and more specifically, joining bell and spigot pipe to withstand forces which are suddenly and strongly applied to the pipes.
2. Description of the Prior Art
It is common practice to make pipe joints wherein one pipe having a spigot or plain end is pushed into the bell end of another pipe. To prevent leakage a soft rubber ring with a hard rubber insert on one side is placed into the bell of the outside pipe, prior to the insertion of the spigot end.
To prevent the pipes from separating under pressure such joints have been modified by using tightening bolts, and tightening plates to connect the pipes. However, these plates and bolts have proven to be costly and complicated to use in the field.
A newer method of connecting such pipes is taught by U.S. Pat. No. 3,684,320. In this patent the outer circumference of the plain end of one pipe has a series of supporting elements and the bell end of the other pipe has at least one projection, protruding downwardly towards the inside of the bell. The diameter of the projection is at least equal to the diametric distance between the outer surfaces of the supporting elements so that the plain pipe with its supporting elements can be pushed into the bell end of the other pipe and inwardly beyond the projection. Locking members are inserted between the projection and the supporting elements to lock the pipe together. The locking members are introduced into a recess or recesses in the projection and rotated to engage a portion of the projection and the supporting elements.
In the disclosure of the prior art U.S. Pat. No. 3,684,320 and, in actual practice, the mating surface of the projection and the locking members have the shape of a spherical shell and both spherical shells have the same diameter. In effect, the two surfaces coact in a wedging action so that as the inner and outer pipes are moved apart by the pressure of the internal fluid, the two mating surfaces slide against each other. Since the projection has a slope slanting downwardly in the direction of the open face of the bell and the locking segments have a slope in the same direction, as the pipes tend to move apart, a compressing action takes place between the projection and the locking segment because the locking segment is held tightly against axial movement by the supporting elements.
While the above described joint is prevalent in the market place, there are certain circumstances wherein the joint becomes subject to sudden unexpected forces which tend to destroy the joint. A particular case occurs when a pipe is subjected to sudden earth movement, such as an earthquake. Under these circumstances even the improved joint may prove inadequate.